Historically, medicinal plants have been used since ancient times. Humans commonly used spices because of their high essential oil content that helped to keep food from becoming diseased by bacteria or other microbes. These herbs and spices have special compounds in them to prevent disease. Today we spice food because we think it tastes good, but it is also helps to keep us healthy. These compounds that prevent microbial infection are usually essential oils which we can smell.
Medicinal plants typically have essential oils in their tissues or seeds that prevent bacteria, molds, or other microbes from growing. This quality confers antimicrobial properties. Common herbs like peppermint, basil, oregano, thyme, and rosemary have essential oils that prevent microbial growth. Oregano in particular has been used to help lessen the effects of bacterial infection by making a tea from its leaves.
Ancient Chinese medicine, still practiced today, utilizes everything from plant leaves to bark when treating illness. Chinese medicine has medicinal combinations to prevent cancer, lessen the effects of menopause, increase fertility, reduce blood pressure, and even make people more alert to help them study for tests or work.